Technical Field
The present invention relates to an audio processing device for synchronizing processes between two audio processors, a method of audio processing, a storage medium, and an electronic musical instrument that uses the audio processing device.
Background Art
In audio effects devices that are built into electronic musical instruments and have a delay feature for applying an echo effect to an input signal, there is a conventionally well-known technology known as tempo synchronization delay that automatically sets a delay time according to the tempo setting of an automatic performance (accompaniment, sequencer, arpeggio, or the like) of the electronic musical instrument such that the delay signal is synchronized with the rhythm of the music (the technology disclosed in Patent Document 1, for example). There are also well-known conventional technologies in which even if a song is currently being played, the content of an effect process is changed if an operation for changing the tempo of the performance is performed (the technology disclosed in Patent Document 2, for example).
When using a tempo synchronization delay feature, setting the delay time to a multiple of one beat such as 1/4 beat, 1/3 beat, 1/2 beat, 2/3 beat, 1 beat, 3/2 beats, 2 beats, or 3 beats, for example, makes it possible to produce an echo effect that coordinates better with the music. Furthermore, there is also a conventionally well-known feature known as a sample looper that uses this delay feature to repeatedly play back the same performance.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. H5-94180
Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2011-215363
However, in conventional tempo synchronized delay features, the delay time is not actually completely synchronized with the tempo of the automatic performance due to discretization of delay time and/or the tempo with a clock or clocks, which are the minimum time units that can be handled in digital data processing. As a result, the discretized delay time is set such that it is synchronized with the tempo (which may also be discretized) within a permissible range. Therefore, strictly speaking, the delay time is actually slightly shifted from the tempo. This shift will generally not be perceived if the amount of feedback in the delay is small or if the repeat count is relatively low. However, if the delay feedback amount is large, the repeat count is high, or the feature is used to implement a sample looper that repeatedly plays back the same performance with the feedback set to 100%, the shift accumulates during each repetition until the error is magnified enough to be audible to the human ear.
The present invention therefore aims to make it possible to correct this shift in timing in automatic performance processes and audio effect processes. Accordingly, the present invention is directed to a scheme that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.